208 Nichols, A morphological study of Juniperus communis var. depressa. 



before the initiation of metakinesis becomes distmctly bipolar 

 (fig. 26). The chromosomes, which after the disappearance of the 

 nuclear membrane have become crowded together, are rapidly 

 oriented toward the nuclear plane and assume a position approxi- 

 mately perpendicular to the axis of the spindle. In this position 

 it is possible, in sections cut perpendicular to the spindle axis, to 

 count twelve chromosomes, which represent the reduced number 

 characteristic of the gametophyte (fig. 27). In the megaspore mother 

 cell of the European J. communis Noren (1907) finds only eleven 

 chromosomes. It is not surprising, however, that there should be a 

 divergence of opinion on this point, since not only are the objects 

 under consideration very niinute, but even in sections which are 

 favorably cut and stained the chromosomes are crowded and usually 

 appear to overlie and merge into one another, so that their accurate 

 enumeration is extremely difficult, nor is it impossible that the 

 number in var. depressa differs from that in the European form. 

 In view of Noren 's results a careful recount was made, but 

 although cases are frequent where only eleven can be seen, in 

 some instances at any rate it was determined with considerable 

 certainty that there are twelve chromosomes. 



The chromosomes are short and thick, but as theylie in the 

 equatoriai plane the various L, V, X, Y, and forms characteristic 

 of the heterotypic division are often recognizable. The spindle 

 fibers are attached at or near the inner ends of the daiighter chro- 

 mosomes, and their Separation begins at this point. During the 

 anaphase the daughter chromosomes are drawn apart and as they 

 approach the poles it can be seen that they have undergone a 

 second longitudinal fission (fig. 28). Just what significance should 

 be attached to this fact is doubtful, but in the light of subsequent 

 events it seems hardly possible that the segments formed at this 

 time are homologous with those of the homotypic division, as is 

 maintained by Strasburger (1900). At the poles the chromosomes 

 come together and form a seemingly homogeneous, lumpy mass in 

 which no structure can be made out (fig. 29). 



The reconstruction of the daughter nuclei is apparently brought 

 about without the formation of a definite spirem, in a manner 

 similar to that described by Lawson (1903) and elaborated by 

 Gregoire and Wygaerts (1904). Lacunae appear within the 

 mass of chromosomes, increase in size, flow together, and force 

 the surrounding chromatin outward (fig. 30). Alveoli then divide 

 the chromatin into smaller masses, until there is formed eventually 

 a well developed resting nucleus in which the identity of the indi- 

 vidual chromosomes is completely lost (fig. 31). Miss Ferguson 

 (1904) finds that in Pinus the chromosomes unite end to end and 

 form a definite spirem which in turn gives rise to the reticulum 

 of the daughter nuclei. There is no stage, however, in the Or- 

 ganization of the daughter nuclei in J. communis where a continuous 

 spirem can be recognized. The nuclei are spheroidal, somewhat 

 broader than long and slightly flattened on the equatoriai surface. 



